Pantograph wearing strip support

ABSTRACT

A pantograph shoe has a plurality of wearing strips each being independently supported by elastic members preloaded against stops to provide a high average force against the contact wire while retaining the desired low spring constant within the working range. The high average force, resulting from a relatively large pre-displacement, counteracts the constant pushup force on the pantograph frame plus the aerodynamic lift of the pantograph plus the dynamic forces due to varying contact wire profile at high speeds. The low spring constant provides for a &#39;&#39;&#39;&#39;soft shoe&#39;&#39;&#39;&#39; which is flexible to the changes in pressure due to variation in the contact wire profile, and it prevents separation that would otherwise occur at high speeds.

United States Patent Gray [ Aug. 20, 1974 PANTOGRAPH WEARING STRIPSUPPORT [75] Inventor: Richard Thurby Gray, Erie, Pa.

[73] Assignee: General Electric Company, Erie, Pa.

[22] Filed: Dec. 20, 1972 [21] Appl. No.: 316,913

Primary Examiner-M, Henson Wood, Jr.

Assistant ExaminerD. W. Keen Attorney, Agent, or Firm-Walter C.Bernkopf; Dana F. Bigelow [5 7] ABSTRACT A pantograph shoe has aplurality of wearing strips each being independently supported byelastic members preloaded against stops to provide a high average forceagainst the contact wire while retaining the desired low spring constantwithin the working range. The high average force, resulting from arelatively large are-displacement, counteracts the constant pushup forceon the pantograph frame plus the aerodynamic lift of the pantograph plusthe dynamic forces due to varying contact wire profile at high speeds.The low spring constant provides for a soft shoe which is flexible tothe changes in pressure due to variation in the contact wire profile,and it prevents separation that would otherwise occur at high speeds.

21 Claims, 12 Drawing Figures PATEN IE0 2 0 i974 SPRING FORCE $830,990SHEEI 20$ .4

FIG. 3

IIIIII b FIG. .5

RANGE OF WORK/N6 DISPLACEMENT RANGE OF FORCE l VARIATION AVERAGESUPPORT/N6 FORCE" CLAMP/N6.

FORCE I i X DISPLACEMENT FROM CLAM PED POSITION P I I PAIENIEBmszomn VRANGE OF won/(we I DISPLACEMENT 1 F/G 9 RANGE 05 FORCE g VARIATION l U IO: l 3 3 o z AVERAGE I E SUPPORT/N6. v FORCE PRELOAD i FORCE 1 i l I 0 vVERTICAL DISPLACEMENT FROM PRELOADED POSITION 0.06- roams LINKAGEAPPLIED rams vs o/s mcsumr 0,05 //v omens/amass ram 1 PANTOGRAPH WEARINGSTRIP SUPPORT BACKGROUND OF THE INVENTION This invention relatesgenerally to power collection systems and more particularly topantographs for transmitting power from a wayside contact wire to a highspeed vehicle.

A customary approach to collecting relatively heavy currents from anoverhead conductor for propelling an electrically operated vehicle, suchas a transit car or comotive is to utilize a current collector of thepantograph type having a plurality of slider shoes mounted on apantograph structure for engaging the contact wire. Because of theirregularities in the construction and suspension of the overheadcontact wire there is a tendency in the pantograph structure of theprior art to move out of engagement with the conductor wire and therebydisrupt the flow of current therebetween. This tendency is accentuatedwith increases in vehicle speed, and may become prohibitive whenoperating at speed ranges in excess of 100 mph. In addition to theincreased relative speed of the engaged catenary and collector shoemembers, with the attendant propensity for separation, the aerodynamicforces acting on the pantograph also affect its disposition with respectto the conductor wire.

Various schemes have been devised to provide the required biasing forceto maintain engagement between the sliding members. Generally, a degreeof resiliency must be provided to allow for slight deviations of contactwire profile and still maintain mutual contact. However, it is foundthat a relatively small biasing force between the collector and thecontact wire is insufficient to maintain the desired contact.Conversely, a relatively small degree of resiliency force is notentirely satisfactory since it does not allow for slight changes in thepantographs postion in response to the small irregularities of thecontact wire.

It is therefore an object of this invention to provide a pantographassembly which is effective in use with high speed vehicles.

Another object of this invention is the provision for maintainingengagement of a high speed pantograph shoe with a wayside contact wirewhose construction and profile have variable characteristics.

Yet another object of this invention is the provision for biasing acollector element against a contact wire to prevent momentary separationdue to the deviation of force therebetween.

Still another object of this invention is the provision for minimizingthe adverse affects of aerodynamic lift of a pantograph as they tend tolift the associated slider shoes toward the engaged contact wire.

A further object of this invention is the provision for a pantographassembly which is simple to fabricate, economical to operate andextremely functional in use.

These objects and other features and advantages will become more readilyapparent upon reference to the following description when taken inconjunction with the appended drawings.

SUMMARY OF THE INVENTION Briefly, in accordance with one aspect of theinvention a plurality of short flat wearing strips are supported by ashoe base with elastic mediums placed therebe-' tween to bias thewearing strips towards the contact wire with which they are engaged. Foreach strip the elastic medium is compressed through a relatively largedisplacement and then clamped against stops to prevent the loss of thisdisplacement but allowing it to be free to displace further. Thedisplacement and spring gradient of the elastic medium is chosen suchthat the force at zero displacement due to clamping the preloadedelastic medium is set to equal the push-up force plus the aerodynamiclift for a relatively slow speed, whereas the average supporting force,as seen by onehalf the total possible displacement from the clampedposition is set to equal the push-up force plus the aerodynamic lift atthe highest desired speed of the pantograph. The result is that arelatively high force is provided to support the force from the contactwire and yet a low spring constant is provided within the working rangeso that the strip is responsive to small changes in this force.

In the drawings as hereinafter described, a preferred embodiment andmodifed embodiments are depicted; however, various other modificationsand alternate constructions can be made thereto without departing fromthe true spirit and scope of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a front view of thepantograph assembly and associated contact wire as contemplated in thepresent invention.

FIG. 2 is a top view thereof showing the wear strip segments.

FIG. 3 is a partial sectional view as seen along line 33 of FIG. 2.

FIGS. 4 and 4A illustrate a modified embodiment thereof.

FIG. 5 is a graphic illustration of the force variation of the elasticmedium as a function of displacement from a clamped position.

FIG. 6 is a partial front elevational view of a modified embodiment ofthe subject invention using torsional springs.

FIG. 7 is a top view thereof.

FIG. 8 is a sectional view thereof as seen along line 8-8 of FIG. 7. 7

FIG. 9 is a graphic illustration of the force variation of the elasticmedium in the embodiment shown in FIG. 4 as a function of displacementfrom a clamped position.

FIG. 10 is a front elevational view of a third embodiment of theinvention utilizing tension springs.

FIG. I l is a graphic representation of the force analysis of a linkageapproximating that in FIG. 10.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FIGS. 1 and 2,a pantograph 10 of the present invention is shown in combination with acontinuous contact wire or contact wire 11 charged with a voltage from awayside power source (not shown) and extending along the longitudinaldirection of travel. The contact wire may be one of any of the waysidepower delivery types; however, that which will be referred to forpurposes of this description and which is particularly suited to usewith the present invention is that of the overhead catenary type,wherein the profile with respect to a horizontal plane is necessarilynon-uniform and further wherein vertical irregu- Iarities exist alongthe length thereof and tend to cause intermittent separation fromfrictional engagement with contact portions of the pantograph 10.

The pantograph 10 is of the type normally mounted to the superstructureof a transit car or locomotive (not shown), and comprises a frame 12extending transversely across the top portion of the car and held up bya constant push-up force mechanism in its base (not shown). Connected toopposite ends 13 and 14 of the frame 12 are spring plunger assemblies 16and 17 respectively having their plungers l8 and 19 extending upwardlyto resiliently support a shoe base 21 with respect to the upper frame12. Increased downward dynamic force resulting from contact with thecontact wire 11 as the vehicle moves will cause the plungers 18 and 19to depress and lower the base 21 with respect to the frame ends 13 and14. When the vehicle is at rest, the force between the contact wire 11and the pantograph wear strips 22 is then constant and is commonlyreferred to as the pantograph push-up force.

Secured to the upper side of the shoe base 21, on a substantiallyhorizontal plane, is a plurality of resiliently supported wear stripsegments 22 electrically connected to the vehicle propulsion system andinsulated from the car superstructure which indirectly supports them.The strips are adapted to maintain frictional contact with the contactwire 11 as the vehicle travels along the wire in a longitudinaldirection. The number of segments 22 is not critical to this inventionnor is the geometric arrangement thereof, that shown being a typicalarrangement having a pair centrally located with respect to the base 21and a pair transversely spaced on each side thereof. Each pair islongitudinally spaced to provide a broad base with which the contactwire 11 can maintain frictional engagement as the contact wire movestransversely across the shoe. As seen in FIG. 1 the segments 22 arestraight along their lengths except those portions proximate their endswhich are curved downwardly to prevent fouling of the contact wire 11 asit moves transversely from one deflected pair to another undeflectedpair. The ends of adjacent pairs also overlap at the curved portions tofurther facilitate a smooth transverse movement of the wire relativethereto. In the embodiment illustrated the wire 11 will generally be incontact with the centrally disposed pair of segments. However, duringperiods in which the pantograph and wire move relatively transversely,as for example when the car leans in rounding a curve, the wire mayslide transversely to the point where it contacts a side pair ofsegments. Outside of these segments on each end of the shoe base 21 isan end horn 23, having its inner end at substantially the same level asthe outer end of its adjacent segments, and having its outer end curvegradually downward. The purpose of the end horns is to allow theconductor wire 11 to slide to the outer sides of the pantograph shoeduring occasional periods of operation, as for example, in a yard, andsubsequently return smoothly to the central portion of the shoe.

The wear strip segments 22 are each secured to the shoe base 21 bylinkage means 24 at each end thereof. The construction of linkage means23 is best understood by reference to FIG. 3 which shows the wear stripsegment 22 mounted to the shoe base 21 by the interconnecting rod 26 andcompression spring 27. The rod 26 is secured at its one end to thesegment 22 by suitable means, such as by a pin 28 passing through therod and secured at its ends to a clevis 29 attached to and extendingdownwardly from the segment 22. The pin is preferably rotatably mountedwith respect to either the base or the rod so as to allow the rod topivot with respect to the segment.

The other end of the rod 26 extends through an aperture 31 in the shoebase 21 and has attached thereto a stop collar 32 secured in aconventional manner by a retaining pin 33. The stop collar 32 is adaptedto be biased upwardly against a base stop 34 which forms that portion ofthe base surrounding the aperture 31. A rebound spring 36 is preferablyinserted between the base stop 34 and the stop collar 32 to reduce shockand chatter when the two elements are intermittently brought together.Also preferred is a guide bushing 37 interfacing the walls of theaperture 31 and the rod 26. The elements of the linkage means 24 areassembled in a manner such that the compression spring 27 isprecompressed in accordance with a predetermined range of force as willbe more fully explained hereinafter.

A modified embodiment of the linkage means is shown at 24 in FIGS. 4 and4A. At the upper end of the rod 26 is a normally extending pivot 38rotatably mounted in a pivot strap 39 secured to the underside of thesegment 22. Abutting the underside of the segment 22 is the top end of aguide tube 41 extending downwardly around the rod 26 and through theaperture 31. The lower end of the guide tube 41 abuts a stop washer 42which in turn abuts the stop collar 32. In place of the rebound springof FIG. 3 a rebound ring 43 of an elastomeric material such as rubber orplastic may be inserted between the base stop 34 and the stop washer 42.

Returning now to a discussion of the compression spring 27, it should bepointed out that any form of an elastic medium may be used for biasingthe wear strip segment away from the base 21. However, an importantaspect of this invention is that in the assembly of the linkage means 24of FIGS. 3 and 4, the elastic medium, or spring in the embodiment shown,is compressed through a relatively large displacement and then clampedby means such as with the stop collar 32, to prevent the loss of thisdisplacement while allowing freedom for further displacement. FIG. 5illustrates the spring force variation as a factor of relativedisplacement of segment and base from the clamped position. It will beseen that in the clamped position, or at X 0, the force of the spring,which is available for counteraction against downward force of theconductor wire, is relatively high, while that force which exists on thespring at the point of maximum displacement is not significantlygreater. Stated in another way, the range of force variation" is smallas compared with the clamping force. The spring constant, which isrepresented by the slope of the curve P, is then relatively low, therebyallowing the spring to be responsive to small changes in force from theconductor wire. On the other hand, the average supporting force whichthe spring will resist is relatively high.

The force from the wire which must be supported by the elastic medium ifthe shoe is to remain soft is that of the constant push-up force of thepantograph frame plus the aerodynamic lift on the complete pantographplus dynamic forces due to varying wire profile. A typical design of thesubject invention would be such that the force at zero displacement dueto clamping would be equal to the push-up force plus the aerodynamiclift for a specified lower speed, as for example, 90 mph. Similarly theAverage Supporting Force as indicated in FIG. 5 could be set to equalthe push-up force plus the estimated aerodynamic lift at the highestexpected speed of the pantograph.

As an example, assume a typical pantograph with a push-up force of 28lbs and an estimated aerodynamic lift of 16 lbs at 90 mph and 50 lbs at160 mph. Assume further that spring gradient of 60 lb/in is desirablefor adequate response. Then the preload force at 90 mph would be 28 16=44 lb and the spring would be compressed 44/60 0.73 in. before it isclamped. The Average Supporting Force at 160 mph would be 28 50 78 lbsand the full compression would be 78/60 1.30 in. Half the Range ofWorking Displacement would be 1.30 0.73 =0.57 in., or the full rangewould be 1.14 inches.

As mentioned hereinbefore, the wire 11 will be in contact principallywith the central portion of the pantograph and specifically with thecentrally disposed wear strip segments. Accordingly, the linkage means24 of FIGs. 3 and 4 need only be installed in the centrally locatedsegments, and at the inner ends of the outside segments. The outer endsof the outside segments are preferably only pivoted and not resilientlyfastened to the base, thereby preventing their moving downwardly whenthe wire moves to that area. If the ends were resiliently supported,like 24, the wire would tend to be below the top surface of the end ofthe horn element 23 and could become fouled even though that portion ofthe horn 23 is curved downwardly similarly to the segment ends asdescribed heretofore. Although the outer segments have no elastic mediumsupport adjacent to the horns, they should be pivotably mounted in amanner similar to that of using a rotatable pin 28 in FIG. 3 so as toallow the segments to tip in their length direction while holding theiralignment with the wire 1 1 in their width direction.

A modified embodiment of the present invention is illustrated in FIGS.6, 7 and 8 wherein the end horn 44 becomes a base element on which thewear strip segments 46 are resiliently supported. The pantograph frame12 and plunger assembly 16 is essentially identical to that of thepreferred embodiment. Pivotally secured to the plunger 18 is a shackle47 interconnecting to a bail 48 extending downwardly and substantially'normal to the end horn 44. The placement of the shackle is such thatwhen the end horn 44 is rotated as a result of the shoe being deflecteddownwardly, the distance between supports as defined by the pivot pins49 on the one end thereof and their symmetrical equivalents on the otherend thereof, is increased proportionately to allow the proper freedom ofmovement in the downward direction.

(Connected to the upper end of the end horn 44 by a pivotal shaft 51 isone end of a center link 52 extending transversely in a substantiallyhorizontal plane, across the path of motion to similarly connect to theopposite end horn. The center link 52 comprises a pair of spaced bodymembers 53 and 54 interconnected by cross ties 56. Secured to the uppersurfaces of body members 53 and 54, as well as to the upper surfaces ofthe oppositely disposed end horns are the wear strip segments 46 whichfrictionally engage the contact wire 11. As can be seen from FIG. 6, theinterconnecting ends of the horn and center link are curved downwardlyand are overlapped to prevent hooking the wire if it tends to slideoutwardly onto the end born 44.

As previously stated the horn 44 and center link 52 are pivotable aboutthe shaft 51. Torsion springs 57 are installed at that shaft so as tobias the center link upwardly, or in a clockwise direction with respectto the shaft 51. The extent to which the relative rotation occurs islimited by mutual impingement of opposing stops 58 and 59 located ondownwward protruding portions of the end horn 44 and center link 52,respectively. The stops 58 and 59, which are preferably of theelastomeric type, allow the torsion springs 57 to be preloaded in amanner similar to that described in the preferred embodiment and tend topreserve the flat arch shape in the preloaded position. In FIG. 9 isgraphically illustrated the estimated spring force variation as a factorof vertical displacement of the center link from the preloaded position.Design parameters may be arrived at by consideration of those factorsand in a manner similar to that set forth in the discussion of thepreferred embodiment.

Another alternative embodiment of the invention is shown in FIG. 10wherein the torsion springs of the FIG. 6 embodiment are eliminated'andinstead tension springs 61 and 62 are installed between the respectivebails 63 and 64 and arms 65 and 66. The tension springs 61 and 62 arepreloaded against the elastic stops in a manner similar to thatpreviously described. The shoe is then in an arched position, and as thedownward force is applied and increased to exceed the preload, the shoedeflects with a relatively soft spring constant. The static equationsfor a linkage geometry that approximates the linkage of FIG. 10 can besolved and the results represented in dimensionless form as shown inFIG. 11.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

l. A current collecting pantograph assembly for the transfer ofelectrical power from a continuous overhead conductor to an electricalvehicle for propulsion in the longitudinal direction comprising:

a. a pantograph frame secured to the vehicle;

b. a shoe base secured to said pantograph frame by resllient means, saidbase having a first stop element attached thereto;

c. at least one wearing strip having a substantially flat top surfacefor maintaining frictional contact with the overhead conductor as saidwearing strip moves in the longitudinal direction of travel;

d. linkage means interconnecting said shoe base and said wearing strip,said linkage means having a second stop element for direct impingementagainst said first stop element; and

e. an elastic medium disposed between said shoe base and said wearingstrip for biasing said wearing strip toward the overhead conducter, saidelastic medium being substantially precompressed to a first positionwherein said first and second stop elements are in direct impingement soas to limit the upward movement of said wearing strip with respect tosaid shoe base, the force of said elastic medium when compressed to saidfirst position being substantially equal to the constant push-up forceof the pantograph plus the aerodynamic lift force resulting frommovement of the vehicle at a predetermined speed, and being furthercompressible to a second position when a downward force is imposed onsaid wearing strip so as to provide a relatively high average forceagainst said wearing strip while retaining a relatively low springconstant between said first and second positions.

2. A pantograph assembly as set forth in claim 1 wherein the force ofsaid elastic medium when compressed to said first position issubstantially equal to a constant push-up force of the pantograph plusthe aero dynamic lift force resulting from movement of the vehicle at apredetermined low speed.

3. A pantograph assembly as set forth in claim 1 wherein the averagesupporting force as defined by that force of the elastic medium whencompressed to a point halfway between said first and second positions isequal to the push-up force plus the aerodynamic lift at a predeterminedhighest expected speed of the pantograph.

4. A pantograph assembly as set forth in claim 1 wherein said wear stripis elongate in form as aligned transversely with respect to thelongitudinal direction of travel, and further wherein said contact wireis free to slide across its length while maintaining constant frictionalengagement therewith.

5. A pantograph assembly as set forth in claim 4 and including an endhorn connected to said shoe base at each end of said wear strip, theends of both the wear strip and the end horns respectively overlappingin a direction transverse to the direction of travel and being turneddownwardly to allow said conductor wire to slide smoothly thereover asit slides in a transverse direction.

6. A pantograph assembly as set forth in claim 4 and including means forrestraining said wearing strip from tipping along its width but allowingpivotal movement, about its ends to permit tipping along its length.

7. A pantograph assembly as set forth in claim 1 and including aplurality of elongate wearing strips extending transversely across saidbase in a continuous single plane, the ends of adjacent strips beingspaced longitudinally turned downwardly, and mutually overlapping in thetransverse direction to allow said conductor wire to slide smoothlythereover as it slides in the transverse direction.

8. A pantograph assembly as set forth in claim 7 and including an endhorn connected to each end of said base so as to overlap at least one ofsaid wear strips the overlapping portions of both the end horn and itsadjacent wear strip being turned downwardly to allow said conductor wireto slide smoothly thereover as it slides in the transverse direction.

9. A pantograph assembly as set forth in claim 8 wherein the portions ofthose wear strips overlapping said end horns are restricted fromreciprocal movement with respect to said base but are permitted torotate relative thereto to allow the opposite end of said wear strip toso reciprocate.

10. A pantograph assembly as set forth in claim 1 wherein said linkagemeans comprises:

a. an elongate rod pivotably secured at its upper end to said wear stripand depending therefrom to slidably extend through an aperture in saidbase; and

b. a collar attached to the lower end of said rod to restrict its upwardmovement to said first position.

11. A pantograph assembly as set forth in claim 10 and including acylindrical guide tube concentrically disposed with respect to said rodbetween said wear strip and said collar and wherein said elastic mediumcomprises a helical spring concentrically disposed on the outer side ofsaid cylindrical guide, between said wear strip and said shoe base.

12. A pantograph assembly as set forth in claim 1 wherein said shoe basecomprises a pair of spaced outer members aligned in the transverseplane, said outer members being pivotably secured at their inner ends toopposite ends of said wear strip and pivotably secured at distal pointsthereon to said pantograph frame, and wherein said elastic medium tendsto cause said members to rotate with respect to said wear strip so as tobias said wear strip upwardly.

13. A pantograph assembly as set forth in claim 12 wherein said elasticmedium comprises a torsion spring disposed at the inner ends of each ofsaid outer members and interacts with the wear strip and the respectiveouter member.

14. A pantograph assembly as set forth in claim 12 wherein said wearstrip includes an arm extending downwardly from each end thereof andfurther wherein said elastic medium comprises a tension springinterconnecting each of said arms with its adjacent outer member at apoint removed from its inner end.

15. A current collecting pantograph assembly for the transfer ofelectrical power from a continuous overhead conductor to an electricalvehicle for propulsion in the longitudinal direction comprising:

a. a pantograph frame secured to the vehicle;

b. a shoe base secured to said pantograph by resilient means;

at least one elongate wearing strip aligned transversely with respect tothe longitudinal direction of travel and having a substantially flat topsurface for maintaining frictional contact with the overhead conductoras said wearing strip moves in the longitudinal direction of travel,with the contact wire being free to slide across the length of saidwearing strip while maintaining constant frictional engagementtherewith;

d. an end horn connected to said shoe base at each end of said wearstrip, the ends of both the wear strip and the end horns respectivelyoverlapping in a direction transverse to the direction of travel andbeing turned downwardly to allow said conductor wire to slide smoothlythereover as it slides in a transverse direction, and

e. linkage means interconnecting said shoe base and said wearing strip.

16. A current collecting pantograph assembly for the transfer ofelectrical power from a continuous overhead conductor to an electricalvehicle for propulsion in the longitudinal direction comprising:

a. a pantograph frame secured to the vehicle;

b. a shoe base secured to said pantograph frame by a resilient means andc. a plurality of elongate wearing strips extending transversely acrosssaid base in a continuous single plane, the ends of adjacent stripsbeing spaced longitudinally turned downwardly, and mutually overlappingin the transverse direction to allow said conductor wire to slidesmoothly thereover as it slides in the transverse direction, and

d. linkage means interconnecting said shoe base and said wearing strip.

17. A current collecting pantograph assembly as set forth in claim 16and including an end horn connected to each end of said base so as tooverlap at least one of said wear strips the overlapping portions ofboth the end horn and its adjacent wear strip being turned downwardly toallow said conductor wire to slide smoothly thereover as it slides inthe transverse direction.

18. A current collecting pantograph assembly as set forth in claim 17wherein the portions of those wear strips overlapping said end horns arerestricted from reciprocal movement with respect to said base but arepermitted to rotate relative thereto to allow the opposite end of saidwear strip to so reciprocate.

19. A current collecting pantograph assembly for the transfer ofelectrical power from a continuous overhead conductor to an electricalvehicle for propulsion in the longitudinal direction comprising:

a. a pantograph frame secured to the vehicle;

b. at least one wearing strip having a substantially flat top surfacefor maintaining frictional contact with the overhead conductor as saidwearing strip moves in the longitudinal direction of travel;

c. a shoe base secured to said pantograph frame by resilient means, saidshoe base comprising a pair of spaced outer members aligned in thetransverse plane and being pivotally secured at their inner ends toopposite ends of said wear strip and pivotably secured at distal pointsthereon to said pantograph frame;

d. linkage means interconnecting said shoe base and said wearing strip;and

e. an elastic medium disposed between said shoe base and said wearingstrip tending to cause said outer members to rotate with respect to saidwear strip so as to bias said wear strip toward the overhead conductor.

20. A current collecting pantograph assembly as set forth in claim 19wherein said elastic medium comprises a torsion spring disposed at theinner ends of each of said outer members and interacts with the wearstrip and the respective outer member.

21. A current collecting pantograph as set forth in claim 19 whereinsaid wear strip includes an arm extending downwardly from each endthereof and further wherein said elastic medium comprises a tensionspring interconnecting each of said arms with its adjacent outer memberat a point removed from its inner end. =l=

1. A current collecting pantograph assembly for the transfer ofelectrical power from a continuous overhead conductor to an electricalvehicle for propulsion in the longitudinal direction comprising: a. apantograph frame secured to the vehicle; b. a shoe base secured to saidpantograph frame by resllient means, said base having a first stopelement attached thereto; c. at least one wearing strip having asubstantially flat top surface for maintaining frictional contact withthe overhead conductor as said wearing strip moves in the longitudinaldirection of travel; d. linkage means interconnecting said shoe base andsaid wearing strip, said linkage means having a second stop element fordirect impingement against said first stop element; and e. an elasticmedium disposed between said shoe base and said wearing strip forbiasing said wearing strip toward the overhead conducter, said elasticmedium being substantially precompressed to a first position whereinsaid first and second stop elements are in direct impingement so as tolimit the upward movement of said wearing strip with respect to saidshoe base, the force of said elastic medium when compressed to saidfirst position being substantially equal to the constant pushup force ofthe pantograph plus the aerodynamic lift force resulting from movementof the vehicle at a predetermined speed, and being further compressibleto a second position when a downward force is imposed on said wearingstrip so as to provide a relatively high average force against saidwearing strip while retaining a relatively low spring constant betweensaid first and second positions.
 2. A pantograph assembly as set forthin claim 1 wherein the force of said elastic medium when compressed tosaid first position is substantially equal to a constant push-up forceof the pantograph plus the aerodynamic lift force resulting frommovement of the vehicle at a predetermined low speed.
 3. A pantographassembly as set forth in claim 1 wherein the average supporting force asdefined by that force of the elastic medium when compressed to a pointhalfway between said first and second positions is equal to the push-upforce plus the aerodynamic lift at a predetermined highest expectedspeed of the pantograph.
 4. A pantograph assembly as set forth in claim1 wherein said wear strip is elongate in form as aligned transverselywith respect to the longitudinal direction of travel, and furtherwherein said contact wire is free to slide across its length whilemaintaining constant frictional engagement therewith.
 5. A pantographassembly as set forth in claim 4 and including an end horn connected tosaid shoe base at each end of said wear strip, the ends of both the wearstrip and the end horns respectively overlapping in a directiontransverse to the direction of travel and being turned downwardly toallow said conductor wire to slide smoothly thereover as it slides in atransverse direction.
 6. A pantograph assembly as set forth in claim 4and including means for restraining said wearing strip from tippingalong its width but allowing pivotal movement, about its ends to permittipping along its length.
 7. A pantograph assembly as set forth in claim1 and including a plurality of elongate wearing strips extendingtransversely across said base in a continuous single plane, the ends ofadjacent strips being spaced longitudinally turned downwardly, andmutually overlapping in the transverse direction to allow said conductorwire to slide smoothly thereover as it slides in the transversedirection.
 8. A pantograph assembly as set forth in claim 7 andincluding an end horn connected to each end of said base so as tooverlap at least one of said wear strips the overlapping portions ofboth the end horn and its adjacent wear strip being turned downwardly toallow said conductor wire to slide smoothly thereover as it slides inthe transverse directiOn.
 9. A pantograph assembly as set forth in claim8 wherein the portions of those wear strips overlapping said end hornsare restricted from reciprocal movement with respect to said base butare permitted to rotate relative thereto to allow the opposite end ofsaid wear strip to so reciprocate.
 10. A pantograph assembly as setforth in claim 1 wherein said linkage means comprises: a. an elongaterod pivotably secured at its upper end to said wear strip and dependingtherefrom to slidably extend through an aperture in said base; and b. acollar attached to the lower end of said rod to restrict its upwardmovement to said first position.
 11. A pantograph assembly as set forthin claim 10 and including a cylindrical guide tube concentricallydisposed with respect to said rod between said wear strip and saidcollar and wherein said elastic medium comprises a helical springconcentrically disposed on the outer side of said cylindrical guide,between said wear strip and said shoe base.
 12. A pantograph assembly asset forth in claim 1 wherein said shoe base comprises a pair of spacedouter members aligned in the transverse plane, said outer members beingpivotably secured at their inner ends to opposite ends of said wearstrip and pivotably secured at distal points thereon to said pantographframe, and wherein said elastic medium tends to cause said members torotate with respect to said wear strip so as to bias said wear stripupwardly.
 13. A pantograph assembly as set forth in claim 12 whereinsaid elastic medium comprises a torsion spring disposed at the innerends of each of said outer members and interacts with the wear strip andthe respective outer member.
 14. A pantograph assembly as set forth inclaim 12 wherein said wear strip includes an arm extending downwardlyfrom each end thereof and further wherein said elastic medium comprisesa tension spring interconnecting each of said arms with its adjacentouter member at a point removed from its inner end.
 15. A currentcollecting pantograph assembly for the transfer of electrical power froma continuous overhead conductor to an electrical vehicle for propulsionin the longitudinal direction comprising: a. a pantograph frame securedto the vehicle; b. a shoe base secured to said pantograph by resilientmeans; c. at least one elongate wearing strip aligned transversely withrespect to the longitudinal direction of travel and having asubstantially flat top surface for maintaining frictional contact withthe overhead conductor as said wearing strip moves in the longitudinaldirection of travel, with the contact wire being free to slide acrossthe length of said wearing strip while maintaining constant frictionalengagement therewith; d. an end horn connected to said shoe base at eachend of said wear strip, the ends of both the wear strip and the endhorns respectively overlapping in a direction transverse to thedirection of travel and being turned downwardly to allow said conductorwire to slide smoothly thereover as it slides in a transverse direction,and e. linkage means interconnecting said shoe base and said wearingstrip.
 16. A current collecting pantograph assembly for the transfer ofelectrical power from a continuous overhead conductor to an electricalvehicle for propulsion in the longitudinal direction comprising: a. apantograph frame secured to the vehicle; b. a shoe base secured to saidpantograph frame by a resilient means and c. a plurality of elongatewearing strips extending transversely across said base in a continuoussingle plane, the ends of adjacent strips being spaced longitudinallyturned downwardly, and mutually overlapping in the transverse directionto allow said conductor wire to slide smoothly thereover as it slides inthe transverse direction, and d. linkage means interconnecting said shoebase and said wearing strip.
 17. A current collecting pantographassembly as set forth in claim 16 and including an enD horn connected toeach end of said base so as to overlap at least one of said wear stripsthe overlapping portions of both the end horn and its adjacent wearstrip being turned downwardly to allow said conductor wire to slidesmoothly thereover as it slides in the transverse direction.
 18. Acurrent collecting pantograph assembly as set forth in claim 17 whereinthe portions of those wear strips overlapping said end horns arerestricted from reciprocal movement with respect to said base but arepermitted to rotate relative thereto to allow the opposite end of saidwear strip to so reciprocate.
 19. A current collecting pantographassembly for the transfer of electrical power from a continuous overheadconductor to an electrical vehicle for propulsion in the longitudinaldirection comprising: a. a pantograph frame secured to the vehicle; b.at least one wearing strip having a substantially flat top surface formaintaining frictional contact with the overhead conductor as saidwearing strip moves in the longitudinal direction of travel; c. a shoebase secured to said pantograph frame by resilient means, said shoe basecomprising a pair of spaced outer members aligned in the transverseplane and being pivotally secured at their inner ends to opposite endsof said wear strip and pivotably secured at distal points thereon tosaid pantograph frame; d. linkage means interconnecting said shoe baseand said wearing strip; and e. an elastic medium disposed between saidshoe base and said wearing strip tending to cause said outer members torotate with respect to said wear strip so as to bias said wear striptoward the overhead conductor.
 20. A current collecting pantographassembly as set forth in claim 19 wherein said elastic medium comprisesa torsion spring disposed at the inner ends of each of said outermembers and interacts with the wear strip and the respective outermember.
 21. A current collecting pantograph as set forth in claim 19wherein said wear strip includes an arm extending downwardly from eachend thereof and further wherein said elastic medium comprises a tensionspring interconnecting each of said arms with its adjacent outer memberat a point removed from its inner end.